Production of sodium carbonate



Dec. 19, 1950 L, RQSENSTElN 2,534,298

PRODUCTION OF SDIUM CARBNATE Filed July 12, 1947 So/.Ur/ow /Va /VOJ /lvL/Qu/o NH3 WATER ALA/VCXE` SOLUTION ,N C02 A/va/V/f/Pfcovfey A/VQZCQJv//Za Hf" Y t J/of Sr/QEAM V Na, C0, /0 H2 0 I N V EN TOR. Z wW/a aJf/yJff/A/ of such :process on aqueous fso'lutions *of which become'very '11er-ge .Ior @a given `produc- Patented Dec. 19 `195 :simi-,lssPAIENT i Oily-FICE (A mooo'rroN or .sommo `'t:manoir-Afro aimons; ,mmmnewyork, u, muoiono July "112, 1947,' 'se'risljuu 760,567

*,'My invention "rate's `L`to the ftif iso- -dium carbonate, "and Ymoreparticularly '5to the yfarcduction of :sodium carbonate V'sodiumcamminate.

'ibonote is the :Solvay process which reacts aqueous solutions' oi"sodium chlor-ide with/ammonia 'and carbon dioxide. Because of jthedependence l A e volumes others, .the provision yof ian4irmamouotl'pi'cnzze'ss. vfor Y* `the tproduction .of substantiallypurefsodium carmonate which .can be conducted dnl-a 'relatively fsma'llplant ibecsuse :it .does not requin `relatively .large volumes @ofwaiter, whic'hhefs ry "lzttlefif nnyobnoxious waste produc-ts,ande-which ntithe time lis '.impk economical 'und' :can -loe conductedlonja 'continuous @ther objects of any become apv"parent from m perusalof the following :de-

scription n The accompanying drawing is zu giow-sheetfof the process ofuny invention '..i-n z its :preferred form, and employing protone'starting .ma-

v 'Ini'genemL :my :process the :prod tion-tof carbonate. :winch :l.subsequently hydrolyzed; 1.the conditions oi lysis being iso montrolledLas 'rto feflecwt crystallizat n of sodium carbom'zte imonohydratethexyilution. mbe .ormutlon of sodium .carbonate fmonohwydrate 1an.important `.fiest-ure of tmy because such procedurensures :7a.fdesirnible `"solt #for fthe .soda-rash, Without lmposlng um excessivemater @load vwhen :conversion of the d ysul-t ito :an-

hydrous Ysoun-1m lcartwrm'te is effected, -'a:s would otherwise be the'with mpc to Plug-her hyomd sans vor .sodium 1cm-monsite' mme the'hydrolysis for :seam .webmestre-1m v :form sodium .carbonate 'k broadreerred 'i-nv the :patent fart, fl'luve4 freund otr-unless :such`hydrolysis :is icontluctex'i onde the :control-led iconditons :morel:lolly .discussed Minnfte'rjiit v.yielxl. .other lorador-:las than.sodium lcaxbonnte,

sepemingenehsmamomof moese r1 (C1. 4:ca -essi) prdineto the followingreaction;

other' products ure undesirable when 'substan- 'ti-ellly'pure sodiumcarbonate 'as an fend product fand 'the most 'economical lopere-tionsare `the sims.

TAS vone example, 'hydrolysis of v'sodium .carbamate can yield sodiumbicarbonate whose con- 4version to .fsodium :carbonate must beraccompanied '.by vrecovery and .recycle of .carbon dioxide, .which'-adds complications *in .plant construction,

operation, :and economy. .As :a second example, application fof 'heat toisodium caribamate `-rcem cause a.' .side-'reaction to v4form `sodiumcyanate, as

Y lNouns,co2Jelmer.:NecuoTemo Anysodiuni cyanztte formed Afin continuousoperation 'would 'have to be removed from the circulating solutions "toprevent its voccumulation and contamination of the end-product.

Urea-can 'also form on applicationo 'heat oc- 'andjany urea formed willaccumulate `als an imvplllfy.-

Whenjhydrolysis of sodiumlcarbalmate is carried on vin aqueous 'solutionat ."suiciently high temperature, only "sodium carbonate Tis formed;

AVery-pure form. Thus evaporation of solution to -e'ifect Arecoi'nry isavoided, 'and no "recrystalli'zation 'or otherpurication process need'be applied "to Atice-solid 'sodium carbonate 'mono'hydrate to ''sttelin:soda-ash zof commercial 'grad/e.

Methods of producing sodium Vcertamente are Well .know'noas aredescribed in .the patents to Mittasc'h et al. No. 1,948,002, February20, 1934; 'Thorsse'll et 'a'L No. .2,0'02i681, 'May 28, '1935; and StockNo. v$014,512, 'September 117, T935; 'and any suitable method :may Ebe`employed 'in lmy process for the production of ythe sodium carbamate.However, I preferably produce the sodium can barna'te by reaction ofliquid substantillyianhydrous ammonia.,'-carbon-dioxide or 'a `suitablelcerrbon dioxide containing ,gas (hereinafter both referred togenerically as carbon dioxide), and sodium nitrate ddissolved:in'suc'hliquid ammonia.. Thisf'iis {sobecause "upon separation *of kthe sodium'lcagrba'mofte f'from thereaction vessel, the "''l'trate nn'dwa'shingsresulting I'from the sodium carl 'bamate fproclfuc'tion, provide asource of ernme- M .mum "muore which isy a Avaluable xcorrente-wiel2,534,298 'i it product useful as a fertilizer, among other purposes.Such ammonium nitrate may be recovered by simply evaporating theammonia, and returning it as a recycle. It is also practical to marketthe solution of ammonium nitrate in ammonja for fertilizer use as suchwith or without the addition of water.

The reaction which occurs is as follows:

Although it is preferred to obtain the reaction by dissolving thesod-ium nitrate in liquid ammOIlia, and passing the Carbon diOXde intoth" tion, and crystallization from a saturated solusolution, the carbondioxide can just as well-A be absorbed separately in liquid ammonia,forming a solution of ammonium carbamate which" is soluble in liquidammonia, to which is added or: which is added to a solution ofsodiumvnitrate in liquid ammonia, resulting in substantially lquantitative precipitation of sodium carbamate. I-n either case, thereaction can be conducted-in a suitable pressure vessel from which inertgases :bearing ammonia can be kept under control for recovery andrecycle. Since the reaction with carbon dioxide evolves heat, cooling atthe carbamate reactor is desirable, -Y

Instead of sodium nitrate as thevsource of the sodium salt, anyy othersuitable sodium salt soluble in liquid ammonia may be utilized in itsplace, such as sodium chloride.

carbamate reactor in a form which iilters readily; ff 7 and can beeasily washed with liquidammonia to Afree it from adhering nitratesalts. 4Hence, separation of the sodium carbamate from the reactingmaterials may be readily effected.

rAfter separation of the sodium carbamate from .i

thel carbamate reactor, Iit together with water-is continually orcontinuously introduced into` another vessel wherein it is hydrolyzedunder such controlled conditions as to produce continuously sodiumcarbonate monohydrate :which is the only Y stable,solid crystalline formof sodium carbonate in the solution; the hydrolysis decomposition lbeingrepresented'as follows:

Sodium carbonate crystallizes as salts having .different quantities ofwater of crystallization, such as sodium carbonate monohydrate j:

sodium carbonate heptahydrate (NazCaTI-IQO), and sodium carbonatedeca-hydrate i WeCo-1.10m@ j By controlling the hydrolysis conditionsofthe sodium carbamate, so that crystallization of `sub- -stantiallyonly the monohydrate is eflectedya minimum water load is imposed on thenext lstep of conversion of the hydrated sodium carbonate jtoanhydroussodium carbonate or soda-ash, by

However, so-.: .dium chloride is not as desirable as sodiumniapplication of heat. Such hydrolysis control is, preferably,accomplished by having the temperature of the carbamate hydrolysissolution such as to favor formation of the sodium carbonate monohydrateso that it will crystallize from a saturated solution thereof, and by socontrolling the water balance of the solution by adjustment of thequantity of water fed thereto, as to cause it to be in equilibrium withsodium rated withresp'ect to the monohydrate.

The sodium carbonate monohydrate formation'fthereof, will occur at anelevated tempera- A ture of approximately thirty-two degrees centigrade(B2i-CJ) and above. In a short range below this temperature, theheptahydrate will form, while at still lower temperatures thedecahydrate will form. Hence, this conversion of the sodium carbamate tothe sodium carbonate monohydrate should beata tempera-turewell above lthe critical temperature `Howeverftoinsure formationof the desiredmonohydratdl prefer,- ably carry out the conversion of the carbamatetothe sodium carbonate monohydrate by applying -heat to the` solution tomaintain it at; its boiling point. This ,could be done in a vessel atatmospheric pressure,ibut to hasten the reaction and also to red-uce4vtheV size of the-vessel, I prefer to conduct thedecomposition in aclosed vessel at super-"atmospheric -pressure lin which the solution ismaintained atits'boilingpoint by application of heat. For example,pressurev of about fifty (50) poundspersquare inch is satisfactory,but'the actual'pressure chosen will-depend upon the' residence Itimelallowed; the higher the pressure and the corresponding temperature,.the faster the reaction.

I 4In -any event;v it Yis only -important While the crystals of'sodiumicarb'onate-monohydrate are in contact with' thea'queoussolution, that `the 'temperature be'rnaintained above the transitiontemperaturefofithe monohydrate to any ofI the 'higher hydrates of thesodium carbonate. Formation 'of suchihighe'r Yhydrate is not onlyundesirable because" of vthe imposition 'of an `un- -necessary water'lo'adf-Fin the `conversion "step to the anhydrous sodium"carbonate,`which is efiectedV by application of heat, butalso because of the Wellknown cementing tendency'of such sipectl to 'thesodiuir'rarbonatemonohydrate, and thus cause continual crystallization of suchs'alt, the'quantity' of" water continually' fed into the carbamatedecompsitiorrreaction vessel mustbe so ivcontrolledl' or adjusted v"as"to maintain the proper waterbalance lfor formation of the' sodiumcarbonatemonohydrate As noted from the `vcle-- composition reaction,ammonia and carbon "dioxide are formed; also waterv vapor willnecessarily evolve, "and the formation of sodium carbonatermonohydrattakes up .water 'and willv have adherentwater. "These quantities ofwater leave the vessel. lThe' ammonia and carbon dioxide are recoveredfor recycle irrfan'y suitable equipment as illustrated on'theflow-sheet. i

The crystallineL sodi-um; carbonate `monohydrate remains: injsuspension, and is continually removed in any-suitable manner, lsuch asVby passing.- the Suspension through/settling tanks, and eventuallyfiltering. Transformation of the sodium-carbonatemonohydrate to theanhydrous sodium.rcarbonate, or soda-ash, can be 'readilyaccomplished'byl simply vdriving off the water 'of crystallization, byapplication of heat to any suitable vessel into which the monohydrate isintroduced and in which the contents are preferably maintained underagitation. The specic manner of applying the heat and the degree ofagitation during the heating determine the density of the nal product toa considerable extent.

Although the described method will effect crystallization of sodiumcarbonate monohydrate in substantially pure form, ammonia solubleimpurities from the raw materials will gradually accumulate in thesodium carbonate liquor in the carbamate decomposition vessel, and maybecome occluded in the monohydrate crystals. My method, however,presents aiconvenient way for obviating such occlusion, as I preventaccumulation of such impurities in the solution, by continually removingportions thereof. Sodium carbonate is recovered from the removedportions by passage thereof to a suitable cooler maintained at atemperature at which a hydrate of duction of caustic soda by reactionwith lime, in

any suitable manner, or if desired, additional sodium carbonatedecahydrate can be recovered from such liquor upon leaving the cooler,by cooling the less concentrated liquor to still lower temperatures.

For convenience, I prefer to eiect removal of the impurities bycontinuously tapping off a side stream of the monohydrate suspension asit leaves the carbamate decomposition vessel, as is illustrated by thenow-sheet.

I claim: A continuous method of preparing substantially pure anhydroussodium carbonate which comprises continually introducing sodiumCarbamate and water into a saturated aqueous solution of sodiumcarbonate to eiect hydrolysis of said sodium carbamate whereby sodiumcarbonate monohydrate is the only solid product of hydrolysis;maintaining said solution saturated with respect to said sodiumcarbonate monohydrate to maintain solid phase sodium carbonatemonohydrate continually suspended in said solution, by so controllingthe quantity of water introduced as to cause said solution to becontinually in equilibrium with said solid phase sodium carbonatemonohydrate; applying heat to said solution while said sodium carbamateand Water are being introduced to maintain the solution above 32.0 C. tothereby effect-direct onestep crystallization of substantially onlysolid sodium carbonate monohydrate from said saturated solution;continually removing crystallized sodiuin carbonate Inonohydrate fromthe solution; and converting said removed sodium carbonate monohydrateto anhydrous sodium carbonate by application oi heat.

LUDWIG ROSENSTEIN.

REFERENCES CITED The following references are of record in the ille ofthis ypartent:

UNITED STATES PATENTS Number Name Date 1,980,691 MacMullin Nov. 13, 19342,002,631 Thorssell et al. May 28, 1935 2,003,378 MacMullin June 4, 19352,005,868 MacMullin J-une 25, 1935 2,014,512 Stock Sept. 17, 19352,014,536 MacMullin Sept. 17, 1935 2,026,714 Thompson et al. Jan. 7,1936 2,133,455 Keene et al Oct. 18, 1938 2,161,711` Keep et al. June 6,1939 OTHER REFERENCES McPherson and Henderson, "General Chemistry, page518, 3rd ed., Ginn & Co., Boston.

Industrial and Engineering Chemistry," vol. 35, No. 9, Sept. 1943,article entitled Autoclave gear Pressure-Temperature Reactions," pages927,

